What are the differences bewteen using ISOs vs extracting distributions in multiboot LiveUSBs

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I've created a multiboot pendrive with a couple of Linux distributions by using the YUMI tool from pendrivelinux, and by default it extracts the content of the chosen operating system's ISO on a dedicated folder in the destination pendrive; it can also direclty load ISOs stored on the pendrive. Quoting from the site:

Contrary to MultiBootISO's which used grub to boot ISO files directly from USB, YUMI uses syslinux to boot extracted distributions stored on the USB device, and reverts to using grub to Boot Multiple ISO files from USB, if necessary.

From the practical point of view, what are the differences between these two methods? Choosing one over another affects performance or has some other advantages?
The statement above seems to suggest that an extracted distro is a better choice than one run directly from an ISO file (since the latter is used only "if necessary"), but why? What are the benefits?

I'm more interested in system performance or differences after it has booted, rather than the capabilities of Syslinux Vs Grub. In other words, how it is different a system booted from an ISO to another booted from a directory where it was extracted?

Best Answer

I first thought that YUMI extracts the files to the hard disk, but that's not the case. My understanding now is that YUMI can store on the pen-drive either :

  1. The ISO as-is, or
  2. The extracted files from the ISO as a file system within a partition

This is the reason that for booting the extracted files it can use Syslinux, but it needs GRUB to boot from ISO.

I believe that the idea here is to improve performance by avoiding the overhead caused by using the ISO file-system. Apparently, the file-system used for the extracted files is more efficient than the one built into the ISO, which is after-all that of a CD.

There is also probably an additional overhead involved in having a two-level access : USB disk to access the ISO, then accessing the ISO file-system. This might involve virtualization-type overhead by GRUB to make Linux believe that the ISO is in effect a CD.

I have no information about the relative performance of both architectures, extracted vs. ISO, and the improvement (if any) probably heavily depends on the type of work that you do.

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